According to the prior art parisons heated to blowing temperature while carried on blowing mandrels are delivered to a blow wheel and inserted between blow mold sections. After closing the blow mold sections a stretching rod is inserted from below in the parisons, said rod extending through the blowing mandrel. The parison is stretched and blowing air introduced to blow the parison to a hollow article. The supply of blowing air is controlled by a valve which is provided for each blow mold station. This valve must be opened at a predetermined time, must be then maintained open during a predetermined time and must be finally closed again. Furthermore, cylinders to be actuated by pressurized air for actuating the blow mold sections, possibly a bottom mold section and the stretching rod must be provided which cylinders have to be supplied with pressurized air as well.